 ;;; Searching for minimum covers
 
 (defn- covers?
-  "Technical Helper. Tests wheterh all elements in base-set are contained at least one set in sets."
+  "Technical Helper. Tests wheterh all elements in base-set are contained at
+  least one set in sets."
   [sets base-set]
   (if (empty? base-set)
     true


(defn parallel-closures
  "Returns the set of all closures of the closure operator on the given base set.
Computes the closures in parallel, to the extent possible."
  [base clop]
  (loop [n        0
         closures #{(clop #{})}

    (compare-order x y)))

(defn order-by
  "Returns a function on two arguments a and b that returns true if and only if
  b occurs not after a in the given sequence (ascending order.)"
  [sequence]
  (let [pos (zipmap sequence (range))]
    (fn [a b]
